Resin casting - what clay to use for molds?

Discussion in 'Replica Props' started by adamata, Jun 14, 2006.

  1. adamata

    adamata Sr Member RPF PREMIUM MEMBER

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    What is the best clay to use for making RTV molds? (IE what you fill in the bottom of the mold box to make the top half of a two-part mold)

    I have tried a few things with very little success.

    what have you guys used?
  2. Darth Domain

    Darth Domain Well-Known Member

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    <div class='quotetop'>(adamata @ Jun 14 2006, 08:25 PM) [snapback]1261659[/snapback]</div>
    This site should answer your question, they have a forum to, they are very helpful
  3. Wolvster1

    Wolvster1 Sr Member Gone but not forgotten.

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  4. propsculptor

    propsculptor Sr Member RPF PREMIUM MEMBER

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    I use Leisure Clay, it works well with anything and won't react to any materials,
    such as Plastics or Silicones.
  5. blufive

    blufive Sr Member

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    I use Kleen Klay from

  6. LeMarchand

    LeMarchand Sr Member

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    i use the kind of clay you buy for kids. It comes in all those happy colors and doesn't dry out and it doesn't react with silicones.

  7. Macklin

    Macklin Well-Known Member

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    I use Play-Doh.

    It doesn't react, sticks to absolutely nothing and is super cheap.

    It's not good for every use out there, but it's great for small parts.
  8. SG Merc

    SG Merc Well-Known Member

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    As all of the above posts basically say, use a wax based clay that doesn't have any sulfur in it.

    I use an art clay from the craft store. It works the same as Kleen Klay, but ends up costing half the price (with shipping from Mirco Mark etc..).
  9. Fetthunter

    Fetthunter Sr Member

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  10. monstermakerman

    monstermakerman New Member

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  11. Ghost Host

    Ghost Host Sr Member

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    You can use most anything, but I know many FX professionals use WED clay. it's a water based clay made for things such as this.
  12. GuntahKela

    GuntahKela Sr Member

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    I use the green Roma Plastilina bought at art supply stores. Have had my batch for 12 years, and it still works fine.
  13. modelnutz

    modelnutz Member

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    I'm one of those that uses WED clay.
    More specifically, Laguna brand from michaels.
    $6.00 a box.
    The gray type is better than the terra cotta...less stickyness.
    Cleans up with water.
  14. franz bolo

    franz bolo Sr Member

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    Klean Klay. Don't use sulfur based clays.

  15. Blackbirdcd

    Blackbirdcd Well-Known Member

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    I second the KleanKlay suggestion. It handles better than any of the other options.
  16. exoray

    exoray Master Member

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    I use WED as well, from Hobby Lobby, Amaco X-15 potter clay... 25 pound box, normal price is $14.99 but they have 40% coupons almost every week on the website so I only pay $9 a box, and I avoid shipping cost...

    The only issue with the X-15 is that it's not advertised as sulfur free so it would be wise to test your batch first... But, I have used it for several years (multiple batches) for both tin and platinum cure silicone without issue...

    The reason I use WED is simply because it's cheap and I can get it local easily... And the fact that I'm lazy, and prefer to use it once and then simply toss it and get a new batch for the next project, no time spent trying to reclaim it...

    The oil and wax based clays like mentioned above have the advantage that they don't dry out and are easy to reclaim and re-use but they are more costly from the start... They also don't shrink like WED clays, not an issue if you mold right away but if you leave WED exposed to the air for even a few hours it will start to dry out and shrink, and pull away from the object...

    That new elastic Monster Clay looks very interesting, I might have to pick some up and play with it...
  17. division 6

    division 6 Master Member

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    Does the moisture in the WED clay effect the silicon or does it need to be sprayed with a coat of lacquer?
  18. EricHart

    EricHart Member

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    If you ever try a new clay, and it turns out to have sulfur in it, or some other chemical which inhibits your silicone from curing, you may still be able to save your pouring. Remove the clay from the silicone, and let the layer of uncured silicone remain exposed to the air for a few hours; sometimes that's enough for it to fully cure.
  19. Little Fett

    Little Fett Member

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    I use everyday water based for my silicone molds. The texture gets alittle funky in places though (not due to chemical reaction, just the fact that it really captured the exact texture of the clay), so you might wanna go with something alittle more high quality.

    I swear by water based though, but that's probably because I'm just cheap:love.
  20. exoray

    exoray Master Member

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    I have never experienced any adverse results due to the moisture... I never deliberately coat it with any type of sealer, although depending on the part being molded I might dust it with some paraffin release and that inevitably over sprays onto the clay...

    If it has sulfur it in though you could run into some big issues, some tin cure silicone will rough it out and do just fine with sulfur, but not all... And IMO forget about any platinum cure and sulfur, big gooey mess just waiting to happen...
  21. RisingZan

    RisingZan New Member

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    I don't mean to resurrect a dead thread, but I would like to know people's experience with the inverse of the OP question. If I use Clay as the sculpting material, is it okay to use clay to fill the mold box? I imagine it sticking and ruining the sculpt. Or is it simply a difference in clay "stiffness" that will protect me from such a problem?
  22. skynet

    skynet Well-Known Member RPF PREMIUM MEMBER

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    You can use cheap normal water based clay but be sure to seal it with a clear coat (ordinary spray can) so water and sulphur doesn't inhibit the cure of resin or silicone.

    It worked totally fine for me.
  23. KingJawa

    KingJawa Active Member

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    I use monstermakers oil based & water based clay. I like the water base because its much easier to sculpt with. The oil based doesnt dry out but needs to be heated to work well in cold temp. areas.
  24. kelsobrooks

    kelsobrooks Member

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    I have purchased some Klean Klay, can I use it to make the mold for an object and pour resin directly into it....? Or do I have to use something else to make a cast first...? :confused


  25. Imhotep72

    Imhotep72 Active Member

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    I thought about trying that but didn't think it would work; if it does that's a serious money saver! :lol
  26. exoray

    exoray Master Member

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    Depends... As it's a loaded question... There are several way to mold and cast things, not one single right or wrong way or single right or wrong product for every application...

    So yeah you can smash a piece into clay, pull it out and then cast a part in the squished clay... Not the best option most of the time but it works for down and dirty quick casting...

    Clay can be used lots of ways, to build up a part, to sculpt a part, to make walls or what not when casting, to squish molding or to plug a hole...
  27. propsculptor

    propsculptor Sr Member RPF PREMIUM MEMBER

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    Another great Clay to use is "Van Aken Clay" which you can find at any "Michaels" Art supply store, it has No Sulfur in it and does not react to any Silicone at all. It's cheap, smooths easily with Lighter Fluid, and easy to use for anything.

    I've used it for more than 4 years straight at a company where we used various brands of Silicone with No problems at all.
  28. clonesix

    clonesix Sr Member

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    I use water clay, as it is easy and quick to apply, easy to slice through and put a box around. Silicone RTV likes moisture, so it is not a problem. It is also easy to clean off the model.

    All other clays mentioned will also work fine.
  29. Diastrom

    Diastrom New Member

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    It sounds like Klean Klay is quite popular. What consistency do you recommend; soft, medium or hard?
  30. TheSt.LouisKid

    TheSt.LouisKid Sr Member

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    I have not used clay since the mid 90's.
    You make your master correctly and the need for clay is eliminated.
    I don't make parting lines with an xacto either.

    Rubber cement and poster board.
  31. red4

    red4 Sr Member

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    How do you make registry points?
  32. OldSkoolEffects

    OldSkoolEffects Well-Known Member

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    It would seem the rest of the mold-making world is decades behind you, then.

    I use Klean Klay, which now has become some generic gray clay you can get at most craft stores.
  33. TheSt.LouisKid

    TheSt.LouisKid Sr Member

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    Koogly eyes like what you find at the craft store. I'll take a pic of one my molds so you can see. Hard to put into words.
    Zlurpo likes this.


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    I'm looking to sculpt and sculpt a monster head about 3-4 times larger than a human head.

    I'm looking for the best clay for the money that I can later mould with silicone.

    Cost is a factor due to the sheer size, I'll probably build up a base out of foam glued to plywood just to save on volume?

    Any thoughts?
  35. cavx

    cavx Master Member RPF PREMIUM MEMBER

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    I use Plasticine that I got from the school my wife teaches at. Anything the kids get has to be "safe to eat". I ran a small test first up and found no re-actions, and so have continued to use to this day. Plasticine can be a bit hard at time (especially in these cooler months we are having now down under) and I either place it in the microwave for up to 60 seconds or leave it out in the sun for 30min. Once heated, it become very soft and easy to work. Once it cools, it goes back to original hardness it was.
  36. falloutboy

    falloutboy Active Member RPF PREMIUM MEMBER

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    I use the cheap kids modeling clays that are sulfur free.

    Haven't seen a reaction with any silicone yet (6 years of use in molding little bits and scenic pieces for wargaming).

    Plays nice with smooth-on products and is cheap.
  37. Daniel Nelms

    Daniel Nelms Sr Member RPF PREMIUM MEMBER

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    Neropost :)

    I use monster clay, it's soft when heated but hard when it cools and the additional wax they put in it makes it easy for me to smooth out.

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